This invention relates to an evaporator of a vertical type. Highly purified distilled water and pure steam are required at production facilities of various medicaments as well as sites of medical treatments. This invention relates to an improved vertical evaporator adapted for use in connection with an apparatus for producing distilled water or a pure steam generator for the generation of pure steam.
As an example of such an evaporator, Japanese Patent Publication Tokko 57-2041 and U.S. Pat. No. 3,875,017 have disclosed a vertical evaporator comprising an inner tube containing a heat exchanger inside and having a helical flow duct on the outside and an outer tube surrounding this inner tube. Water which is supplied to the interior of the inner tube is heated by the heat exchanger, and the mixture of the pure steam thus generated by the heating and water droplets which have not evaporated is ejected from the bottom of the inner tube. While it rises through the helical flow duct, it is separated into the gas and liquid phases, and the separated water droplets are dropped from small apertures on peripheral surfaces of the duct into a narrow space formed between this helical flow duct and the outer tube, going down to the lower part of the outer tube while the separated pure steam is taken out from the top.
Such a prior art evaporator has several drawbacks. Firstly, since the inner tube having a helical flow duct on its exterior is contained inside the outer tube such that a narrow space is left between the peripheral surface of this duct and the outer tube, the overall structure is complicated, and not only is its production difficult but its maintenance is cumbersome. Secondly, since the separated water droplets are dropped from the apertures around the helical flow duct into this narrow space down to the lower part of the outer tube, dirt will tend to accumulate easily between the helical flow duct and the outer tube while its thorough cleaning is very difficult to carry out.